10
TROUBLE SHOOTING
Philosophy
Effective trouble shooting requires that problem locations
be systematically eliminated until the problem is found.
There are four basic questions to answer when trouble
shooting (Ref. #1):
1. Did it ever work right?
2. What are the symptoms that tell you it’s not working
right?
3. When did it start working badly or stop working?
4. What other symptoms showed up just before, just
after, or at the same time as the failure?
It is best to write down any clues you may obtain. Be sure
to write down anything unusual.
The response to question #3 should probably not be 3:04
P.M.. A useful response might be, “Just after an electrical
storm.” or, “Just after it fell off the shelf.”
Double check all the simple solutions to the problem
before searching for complex ones. If the problem occurs
right after installation, it probably has a simple solution.
If an automobile engine cranks, but doesn’t start, make
sure there is fuel in the tank before replacing the engine.
If the electronic equipment doesn’t function verify that it
has power and is turned on.
Systems containing parts which can be quickly inter-
changed are easy to trouble shoot. Swap parts until the
problem moves. The location has then been narrowed to
the part that caused the problem to move.
Sometimes there are multiple problems. These reveal
themselves in layers much like peeling an onion.
It often helps to explain the problem to another person,
even if that person is not knowledgeable about the
particular piece of equipment.
This does two things. First it requires you to organize the
situation so it can be explained to another. Secondly, it
may turn out that you are so familiar with the situation that
you have over looked the obvious. Another person
unfamiliar with the equipment may be able to help.
If you are unable to solve the problem, put it aside until
the next day. Some new thoughts will probably occur
while working on another project.
No Rainfall Recorded
All Switches in S1 must be in OFF position.
Debris in gage
Failed Switch in Gage -Use ohm meter to check resistance
as bucket is slowly tipped by hand. Meter should indicate
infinite resistance when bucket is at rest. It should
indicate 1 - 10 ohms when the switch is closed.
Broken Signal Cable - Ohm meter will indicate only
infinite resistance.
Failure of Electronics in Transmitter - Disconnect signal
cable. Use a switch or short piece of wire to momentarily
connect the two terminals on the Transmitter circuit board
at two second intervals. This will simulate pulses from the
rain gage. If the output of the Transmitter fails to respond,
return the Transmitter to the factory for repair.
Excessive Precipitation
Check that the gage orifice is level.
General Electrical Problems
Loop Current Failure Description
0 mA
Current loop polarity reversed
Open circuit in cable
Power supply failure
Less than 4 mA Low power supply voltage
Loop resistance too high
Greater than 20 Short circuit in cable
Does not reach Low power supply voltage
20 mA, otherwise Loop resistance too high
operates properly
References
1. “Troubleshooting is More Effective with the Right
Philosophy”, Robert A. Pease, Electronic Design News,
January 5, 1989.
